Most conventional polymers derived from petroleum resources such as polyethylene terephthalate (PET), nylon, polyolefin and polyvinyl chloride (PVC) resins, have been used for materials for a wide range of applications such as packaging materials. However, these polymers are resistant to biodegradation and related to environmental issues like carbon dioxide gas, which causes the global warming on the waste treatment processes. In addition, there have been wide studies on the use of biomass-based resins showing biodegradability, polylactic acid resin representatively, following the depletion of petroleum resources.
However, as polylactic acid derived from plants is lower in heat resistance, mechanical properties, and the like than petroleum-based resins, there have been limitations of the fields and applications to which it is applicable. Particularly, attempts have been made to use polylactic acid resins as packaging materials such as packaging films, but they have failed due to the poor flexibility of polylactic acid resins.
In order to overcome the problems of polylactic acid resins, it has been suggested that low-molecular weight flexibilizers or plasticizers be added to polylactic acid resins, or plasticizers produced by addition polymerization of polyether-based or aliphatic polyester-based polyol be applied to the polylactic acid resins.
However, there is little improvement of flexibility in most of the packaging films comprising polylactic acid resins which are produced according to these methods. Moreover, the films are unsuitable for packaging materials because the films show poor stability as the plasticizers bleed out and contaminate the packaged contents over time. Furthermore, the packaging films have the disadvantages of an increase in haze together with a decrease in transparency. In most cases of conventional methods, the films are unsuitable as packaging materials because an improvement in flexibility of the films results in a great decrease in mechanical properties or anti-blocking properties.
Accordingly, there is a continuous demand for a packaging film which has optimized properties such as excellent flexibility, mechanical properties, stability, and transparency as well as biodegradability.